Gut infections in mammals, and in particular humans, stimulate an immune response in mucous secretions, such as saliva, through activation of the common mucosal immune system. This response often initially parallels an antibody response in serum although is generally characterised by the presence of IgA antibodies. However, the immune response in secretion, including saliva, rapidly diminishes following elimination of the antigen (e.g., bacteria or virus) from the body. Accordingly, the presence of antibody in mucous secretions reflects current, i.e., contemporary, infection. In the case of a microbial infection, for example, antibodies in mucous secretions, hereinafter referred to as secretious antibodies, reflect the current status of colonisation of the microbe, such as in the gut, and thus is a useful monitor of contemporary infection. Serum antibody, on the other hand, persists for some time after the microbe is eliminated from the body. A positive serum antibody test, therefore, reflects both past and present exposure to antigen which is less helpful to the clinician. A positive secretious antibody test, on the other hand, indicates present or contemporary infection by the microbe.
The present invention arose following an investigation into Helicobacter pylori (also known as Campylobacter pylori) infection in the gut of mammals. The diagnosis of H. pylori infection can be made by microscopy, microbiological culture or urease detection in gastric mucosal biopsies, urea breath test or by the presence of specific antibodies in serum ELISAs. It might be predicted that H. pylori infection, being an infection of the gastric mucosa, would elicit an IgA antibody response in gastric secretion. However during work leading up to the present invention, it has been surprisingly discovered that the H. pylori specific antibody in mucous secretions is of the IgG class and not IgA as might have been expected. Little IgA antibody, if any, is detected. Accordingly, the present invention is directed to the detection of IgG in mucous secretion specific to H. pylori antigen and thereby provides a means of monitoring current, i.e., contempory infection by that microorganism in mammals.
A test currently available is the CLOtest (registered trademark of Delta West, Ltd., Perth, Western Australia) which detects the presence of urease in biopsy specimens. Although CLOtest is an effective monitor of H. pylori infection, it requires an invasive procedure, i.e., the collection of a biopsy.
In accordance with the present invention, there is provided a rapid in vitro test for contemporary H. pylori infection by determining the presence of specific antibodies, and in particular IgG antibodies, to the microbe in mucous secretions and thereby obviating the need for an invasive procedure.